Codex switch: translate settings-index ↔ rotation-index by auth path (#51)

settings-store lists codex accounts as
  index 0 = ~/.codex/auth.json (default)
  index N = ~/.codex-accounts/{N}/auth.json
but codex-token-rotation only loads ~/.codex-accounts/{N} when those
dirs exist (it ignores ~/.codex/auth.json in that mode), so the
rotation array's indices are off-by-one vs settings indices.

Old buggy behavior:
- "사용중" badge pointed at the wrong account.
- Clicking 전환 on UI #N called setCurrentCodexAccountIndex(N) which
  selected rotation array element N — typically a different
  ~/.codex-accounts/{N+1} entry. Effectively the UI told us a
  different account was now active than what the next codex spawn
  actually used.

Fix
- New findCodexAccountIndexByAuthPath(path) on the rotation module
  exposes a path-based lookup.
- New getActiveCodexSettingsIndex() / setActiveCodexSettingsIndex(idx)
  in settings-store translate via codexAuthPath() ↔
  findCodexAccountIndexByAuthPath().
- /api/settings/accounts.codexCurrentIndex and PUT
  /api/settings/accounts/codex/current both go through the
  settings-side translation, so UI indices are now authoritative.

Co-authored-by: Claude Opus 4.7 <noreply@anthropic.com>

src/codex-token-rotation.ts

@@ -261,6 +261,16 @@ export function getCurrentCodexAccountIndex(): number {
   return accounts.length === 0 ? 0 : currentIndex;
 }
 
+/** Find the rotation-array index that owns the given auth.json path. */
+export function findCodexAccountIndexByAuthPath(
+  authPath: string,
+): number | null {
+  for (let i = 0; i < accounts.length; i += 1) {
+    if (accounts[i]?.authPath === authPath) return i;
+  }
+  return null;
+}
+
 /** Manually switch the active codex account. Clears its rate-limit cooldown. */
 export function setCurrentCodexAccountIndex(targetIndex: number): void {
   if (accounts.length === 0) {